Field of the Invention
The present invention relates to a method for cleaning and drying a semiconductor substrate onto which a pattern has been formed.
Description of the Related Art
In 1980's, light exposure using a g-beam (436 nm) or an i-beam (365 nm) of a mercury lamp has widely been used for resist patterning. As a means for further finer patterning, a method for shifting to a shorter wavelength of exposure has been considered to be effective, so that in a mass-production process after a DRAM (dynamic random access memory) of a 64M bit (work size is 0.25 μm or less) in 1990's, a KrF excimer laser (248 nm) at a shorter wavelength was used as an exposure light source instead of the i-beam (365 nm). However, in production of DRAMs at integration degrees of 256M and 1 G or higher which require a finer processing technique (work size is 0.2 μm or less), light sources at a shorter wavelength were required, thereby a photolithography using an ArF excimer laser (193 nm) has been earnestly investigated in the past ten years. At first, the ArF lithography was intended to be firstly applied to a device fabrication of a 180 nm node device, but the KrF excimer lithography was prolonged in life to a mass-production of a 130 nm node device, so that the ArF lithography was firstly and fully applied to a 90 nm node. Further, such a technique was combined with a lens having an NA increased to as great as 0.9, thereby conducting a mass-production of a 65 nm node device. For the next 45 nm node device, further shortening of a wavelength of the exposure light was progressing and the F2 lithography with a wavelength of 157 nm was considered to be a candidate. However, development of the F2 lithography has stopped due to various problems such as an increased cost of a scanner since an expensive CaF2 single crystal is used for a projection lens with a large amount, an optical system shall be changed accompanying with introduction of a hard pellicle instead of a soft pellicle having extremely low durability, etching resistance of the resist film is lowered, etc., whereby an ArF liquid immersion lithography has been introduced.
In the ArF liquid immersion lithography, water having a refractive index of 1.44 was introduced between a projection lens and a wafer by a partial fill method, thereby enabling a high-speed scanning to conduct mass-production of a 45 nm node device by means of a lens having an NA of about 1.3.
As a lithography technology for 32 nm node, an extreme ultraviolet (EUV) lithography with a wavelength of 13.5 nm has been mentioned as a candidate. As problems of the EUV lithography, there may be mentioned a laser to be increased in output, a resist film to be increased in higher sensitivity, a resolution to be enhanced, a line edge roughness (LER) to be lowered, a defect-free MoSi laminated mask to be used, reflective mirror aberrations to be lowered, etc., whereby the problems to be overcome are piled up. Thus, in the light exposure used as a general-purpose technique, it is approaching the essential limit of the resolution derived from the wavelength of the light sources.
Even under such a circumstance, high integration of a semiconductor apparatus has advanced, and not only improvement in the integration degree using a planar miniaturization by the above-mentioned light exposure, but also the structure of a three-dimensional semiconductor apparatus is beginning to be proposed. Therefore, the degree of substrate processing in the manufacturing process of a semiconductor apparatus is increased than before, and it has been processed to a substrate (hereinafter referred to as “high aspect substrate”) onto which finer and deeper pattern had been formed.
Such a processing substrate is generally processed by dry etching, and a cleaning and drying step is essential to remove fine particles or contamination, etc., generating in the processing steps from the surface of the substrate to clean the same. In particular, drying step is extremely important to prevent from pattern falling or pattern collapse of the processed substrate, and, for example, it has been proposed a method in which a water component used for cleaning the substrate is removed by using a centrifugal force, or drying after substituted by isopropyl alcohol (Patent Documents 1 and 2), and a method for using various kinds of fluorine compounds (Patent Documents 3 and 4), etc.
However, when such methods are used in the high aspect substrate in recent years, there occurs the problems that falling or collapse of the pattern is occurred at the time of drying, or drying of the cleaning solution is insufficient and water mark, etc., is generated.
Also, as the other methods, a method in which the substrate is cleaned by a supercritical state cleaning solution to prevent from occurring pattern collapse has been proposed (Patent Document 5), but according to this method, a specific apparatus for handling the supercritical state cleaning solution is required, so that there is a problem that the costs become expensive.